The present invention relates generally to power supplies, and, more particularly, to a portable, capacitive power supply for powering a load element, such as a portable radiotelephone.
Portable power supplies are utilized to power many varied electrical devices. In many instances, the use of such a portable power supply to power an electrical device is necessitated in instances in which the electrical device cannot be positioned proximate to a permanent power supply to be supplied power therefrom. In other instances, the use of a portable power supply to power an electrical device is advantageous as the portable power supply enhances the portability of the electrical device. A portable power supply may be positioned proximate to the electrical device, or carried with, or within, the electrical device. The electrical device need not be positioned proximate to a permanent power supply to permit operation of the electrical device, and power cables connecting the electrical device with the permanent power supply are not required.
Conventionally, portable power supplies are comprised of electrochemical materials. Energy is stored in the electrochemical material in the form of chemical energy, and, conversion of the chemical energy into electrical energy caused by reaction of the electrochemical material, provides the power to power the electrical device thereby.
Such conventional, portable power supplies are generically referred to as batteries, and are widely popular both for reasons of availability, convenience, and initial purchase price. A battery, however, (as is also true with other types of portable power sources), is of a limited energy storage capacity. When a battery is coupled to an electrical device and utilized to power the electrical device thereby, the stored energy contained in the battery is converted into electrical energy and discharged therefrom.
After an extended period of use, discharge of the stored energy of the battery depletes the battery of remaining stored energy. Once the stored energy of the battery is depleted below a certain level, replacement of the battery is necessitated to permit continued operation of the electrical device. The frequency with which the battery must be replaced is, of course, dependent upon the battery capacity (i.e., the amount of energy stored in the battery), the energy required to operate the electrical device, and the frequency with which the electrical device is operated.
Nickel-cadmium (Ni-Cd) batteries have been developed and are widely used as portable power sources for the reason that a Ni-Cd battery, once depleted of stored energy, may be recharged simply by connecting the battery to a suitable charging current source for a period of time. Other battery types have similarly been developed which may be recharged once depleted of stored energy. Battery charging apparatus is also known and available to permit such recharging.
However, a rechargeable battery cannot be recharged and reused an unlimited number of times. For instance, a Ni-Cd battery may be typically recharged up to approximately five hundred times. After repeated recharging of the Ni-Cd battery, conversion of the energy of a charging current applied to the battery into stored, chemical energy of the battery is much less efficient. Eventually, efficiency of energy conversion becomes so low that the battery does not become recharged to a significant extent. Therefore, even a rechargeable battery has a limited, practical life.
Additionally, when recharging a rechargeable battery, the rate at which a charging current is applied to the battery must be controlled to prevent damage to the battery. More particularly, the charging current applied to the battery must be less than a certain, maximum level. Because the level of the charging current applied to the rechargeable battery determines the charging rate of the battery, the time required to recharge a battery cannot be reduced below a time period which is dependent upon the maximum current level that may be applied to the battery. Such a minimum time period required to recharge a rechargeable battery, can pose inconveniences. For instance, if only one rechargeable battery is available to power the electrical device, the electrical device cannot be operated prior to expiration of the time period required to recharge the battery.
Still further, when charging a rechargeable battery, such as a Ni-Cd battery, at a maximum, allowable charging rate (to minimize, thereby, the time period required to recharge the battery), application of the charging current to the battery must be terminated once the battery becomes fully charged. Overcharging of the battery at the maximum allowable charging rate can cause gassing, electrolytic venting of the battery, permanent loss of battery capacity, and physical damage to the battery.
Capacitors used to form portable power sources for low power applications are also known. For example, capacitive power sources have been utilized as backup power supplies for integrated circuit memories. Capacitors having capacitances of values great enough to generate current levels to power most electrical devices for extended periods of time, however, have heretofore been impractical for the reason that such capacitors were of significant dimensions. Other of such capacitive power sources are of very high effective resistances, and are similarly impractical for use to generate large current levels.
One electrical device which is oftentimes powered by a portable power supply is a portable transceiver, such as a radiotelephone utilized to communicate in a cellular, communication system. When powered by a portable power supply, the radiotelephone may be positioned at any location throughout a geographical area encompassed by the cellular, communication system.
Operation of the radiotelephone, however, typically requires powering of the radiotelephone at a power of up to three watts. Such a power requirement requires a relatively large battery (both in size and weight) to permit extended operation of the radiotelephone. However, to enhance the portability of the radiotelephone, the battery should be of minimal size and weight. Battery size considerations responsive to such power requirements and the design goal of size and weight minimization conflict. Existing rechargeable battery designs compromise between energy storage capacity and battery size. One commerically available, rechargeable battery is of a design which permits powering of a radiotelephone at a power level of three watts for a period of approximately one and one half hours, and is of a weight of less than six ounces.
To operate the radiotelephone for an extended period of time (i.e., beyond the time period permitted by the energy storage capacity of the battery), a radiotelephone user typically carries a spare, and freshly charged, battery in addition to the primary battery initially utilized to power the radiotelephone. Once the primary battery becomes discharged to a level preventing further operation of the radiotelephone, the battery is replaced with the spare battery to permit, thereby, continued operation of the radiotelephone.
The radiotelephone user may be required to carry more than one spare battery to further extend the period of operation of the radiotelephone if the primary battery cannot be recharged before the spare battery becomes discharged.
Even when a radiotelephone user has access to battery charging apparatus, if the time required to recharge the battery (and the battery, as mentioned hereinabove, cannot be charged at a rate in excess of a certain value) is greater than the operational time period of the radiotelephone permitted by the spare battery, an additional spare battery is required to permit continued operation of the radiotelephone.
In light of the above, it may be discerned that the use of a conventional, rechargeable, electrochemical battery as a portable power source to power a portable electrical device, such as a radiotelephone, is not problem-free. A rechargeable, electrochemical battery may be recharged only a finite number of times, and is therefore of a limited operational life. A rechargeable electrochemical battery, therefore, may not form a permanent portion of the electrical device as the battery must be discarded and replaced when the battery can no longer be recharged. Additionally, the time period required to fully recharge a discharged battery cannot be less than a minimum time period as the charging rate in which a charging current is applied to the battery cannot exceed a maximum level. Still further, a high charging current cannot be applied to the battery once the battery has been fully charged.
What is needed, therefore, is a portable power supply of substantially unlimited life, and of a construction and design which permits recharging thereof, once discharged, at a high charging rate to minimize the amount of time required to recharge the power source.